Add kvm guest memfd related capabilities

[KeyboardNerd]

Summary of the PR

The capabilities are required to properly setup a guest_memfd to provide better host and guest memory isolation. The memory attributes capability returns an integer with each bits representing different configs. For example, the return integer & KVM_MEMORY_ATTRIBUTE_PRIVATE > 0 means the vm is capable of setting memory pages to private.

Requirements

Before submitting your PR, please make sure you addressed the following
requirements:

• All commits in this PR have Signed-Off-By trailers (with
  git commit -s), and the commit message has max 60 characters for the
  summary and max 75 characters for each description line.
• All added/changed functionality has a corresponding unit/integration
  test.
• All added/changed public-facing functionality has entries in the "Upcoming
  Release" section of CHANGELOG.md (if no such section exists, please create one).
• Any newly added unsafe code is properly documented.

[KeyboardNerd]

It's a continued discussion from
#284
I accidentally closed that one :(

[TimePrinciple]

Thanks for this work! While I think you could still reopen a PR if you accidentally closed one, if you still have that branch :) Thus we could avoid throwing out PRs

And could you squash 741fb48, 2523d68, 7283cc6 and 3778efe altogether, otherwise we would break bistability along the way 🙂

[roypat]

Could you also squash all the commits into one?

[roypat]

Hey @KeyboardNerd, are you still interested in landing this?

[KeyboardNerd]

Hey @KeyboardNerd, are you still interested in landing this?

Yup, now I have cycles to finish this up. The failure comes from "Title: Undefined behaviour in kvm_ioctls::ioctls::vm::VmFd::create_device" same as the one I see in the lastest PR: #301. Not sure about the reason.

[roypat]

Thanks for updating this! Let's update the commit message to reflect what's actually happening here (since the code itself isn't directly mentioning any guest_memfd stuff anymore, even though the checking of attribute support remains the motivation for these functions).

The CI failure I think can be fixed by just changing the version in Cargo.toml to 0.19.1. It's weird that cargo audit picks this up, but oh well lol (fixed in main)